1. Field of Invention
This invention relates to a process for the complete neutralization of chlorinated polyvinyl chloride and the product resulting therefrom. More particularly, this invention relates to a process for the neutralization of chlorinated polyvinyl chloride using a weak non-gassing base. In addition, the invention also relates to the improved stable chlorinated polyvinyl chloride formed by said process.
2. Description of the Art
Chlorinated polyvinyl chloride polymers (hereinafter "CPVC") are extremely useful for rigid and semi-rigid applications. For example, these polymers have been used in pipes, duct work, cable jackets, appliance parts, injection molded valve bodies, fittings, sheets for thermo-forming.
Many processes have been developed to form CPVC from polyvinyl chloride. For example, U.S. Pat. No. 4,412,898, incorporated herein by reference, discloses a process which can be used to form CPVC. However, during the formation of CPVC using any of these processes, hydrochloric acid is released during the reaction of chlorine with polyvinyl chloride. In addition, chlorine which did not react with the polyvinyl chloride is usually found along with the hydrochloric acid in the reaction vessel. If the chlorine and hydrochloric acid are not removed, the resulting CPVC resin can degrade and there may be a loss in stability of the resulting polymer. Therefore, several methods have been developed to neutralize CPVC in order to increase the stability of the polymer and prevent its degradation.
Swiss Patent No. 470,427 assigned to Lonza discloses process for the purification of chlorinated polymers. The process comprises treating the chlorinated polymer with water, methanol or ethanol or mixtures thereof together with a base. The treatment is carried out in the temperature range of 50 to 130 degrees Centigrade and pressure of 0.1 to 10 superatmospheres. The organic phrase is distilled off under pressure and the resulting polymer is washed with water and dried.
Similarly, East German Patent No. 257,072 discloses a process forming CPVC which is free of chlorine and hydrochloric acid. The process is a de-gassing process in which dry CPVC is alternatively evacuated and purged with inert gas while in dilute chlorine and fluidized in a moist gas to remove acid. More particularly, CPVC powder is cooled to about 20 to 50 degrees Centigrade after it is removed from the reactor. The CPVC is alternatively purged with nitrogen and subject to vacuum while being kept in an atmosphere of 3-5 volume percent chlorine and 95-97 volume percent inert gas for at least 30 minutes. The CPVC is then fluidized with acid or nitrogen having a moisture content less than 100% and simultaneously heated to a temperature in the range of 40 to 80 degrees Centigrade until the CPVC has a pH of 5.5 to 6.0. The CPVC is then fluidized with acid or nitrogen having a moisture content of one hundred percent until the pH of the powder is 6.1 to 6.6.
Japanese Patent No. 6,129,6004 also discloses a procedure for treating chlorinated vinyl chloride resin to remove the unreacted chlorine and the hydrogen chloride by-product of the chlorination of polyvinyl chloride. The treatment comprises washing the CPVC resin with water and filtering the resin to remove any unreacted chlorine and the hydrogen chloride by-product. The CPVC resin is then shaped into a cake and washed with pure water having a specific resistance of at least 20K Ohm. The CPVC resin is then dried.
Russian Patent No. 895,991 to Voroseva discloses a process for preparing chlorinated PVC. The CPVC prepared by the method is neutralized by sodium thiosulphate or hydrazine after the chlorinated polymer is formed.
U.S. Pat. No. 3,440,236 discloses a method for the separation of CPVC from its solution of tetrachloroethane. The CPVC of this invention is formed as a result of chlorination of polyvinyl chloride dissolved in tetrachloroethane solvent. The solution containing the CPVC is mixed with a non-solvent such as methanol in a controlled manner so as to maintain the methanol in the range of 0.25 to 0.6 by volume while at the same time adding methanol alone or in admixture with tetrachloroethane so as to maintain the volume of tetrachloroethane to methanol in the mixture within the same limits. The CPVC is then separated as a fine powder from the solution of tetrachloroethane.
U.S. Pat. No. 3,551,400 discloses a process for the manufacturing of CPVC. The CPVC polymer after it is formed is subjected to any reducing agent which is capable of reducing the chlorine and/or hypochlorous acid resulting from the chlorination of polyvinyl chloride. The CPVC is subjected to reduction before any chlorine dissolved in the CPVC or hypochlorous acid reacts with the formed CPVC. Any reducing agent can be used as long as it is capable of reducing chlorine and for the hypochlorous acid which is to be removed. The reduced CPVC resin has improved stability.
U.S. Pat. No. 4,374,205 discloses the stabilization of post-chlorinated vinyl chloride polymers by phosphate salts. In this patent, the patent teaches neutralizing the CPVC polymer after the polymer slurry is filtered or centrifuged to free it of the liquid phase and the filtered product is neutralized by the addition of water-soluble alkali such as sodium, ammonia hydroxides, carbonates and phosphates.
Although these methods are useful, there exists a need for an easy, efficient, and nonexpensive method to neutralize CPVC after its formation from polyvinyl chloride.
Accordingly a primary object of the invention is the effectively and efficiently neutralize and treat CPVC resin containing hydrochloric acid.
Another object of the invention is to easily and completely neutralize CPVC polymer.
Still another object of the invention is to neutralize acidic CPVC resin with a weak non-gassing base.
Yet another object of the invention is to produce a stable CPVC polymer without any residual acid.
Still yet an additional object of the invention is to produce a neutralized CPVC polymer.